I'm using RedHat 8.x as DHCP server for our LAN. The DHCP is configured to provide IPs for 10 subnets (192.168.10.xxx-192.168.20.xxx). All subnets should have access to the internet. The internet connection is shared via a ISA-Server (proxy and firewall). The problem is, the RedHat DHCP (and DNS) server crashed some days ago (HD died).

I was able to reconfigure RedHat as DHCP for all subnets but now I need to enter the ISA-Server IP as proxy for all clients. Before the crash there was no need to enter a proxy IP to give clients access to the internet.

My question is: Is there a way to setup the RedHat DHCP server (with additional DNS-Server entries) to grand access to the internet for all clients again? Or do I need to setup a DNS-Server (maybe with DNS caching & forwarding)? And where I find a example config for that kind of network???